1. Field of the Invention
The present invention relates to a can end seaming machine for double-seaming a can end on a can body, and more particularly to an apparatus for automatically lifting and lowering a seaming head into a can end seaming position when a seaming chuck and a seaming roll are to be set in place on the seaming head in a can end double-seaming machine which double-seams a can end on a can body that has been filled with contents such as a beverage, thus producing a sealed can.
2. Description of the Prior Art
Canned foods or beverages are generally prepared either by filling a can body with a processed food or beverage material, deaerating the can body, closing and sealing the filled can body with a can end, and then sterilizing the can, or by filling a can body with a sterilized food or beverage material in a sterilized environment, deaerating the can body, and closing and sealing the can body with a sterilized can end. The cans which have been produced in either of the above processes can be stored for a long period of time.
Sealing can bodies with can ends is effective in fully preventing entry of microorganisms, air, and water into cans for protecting the canned foods or beverages against modification or deterioration of properties. Therefore, the can body sealing process is as important as the deaerating and sterilizing processes in making canned foods or beverages resistant to changes in long-term storage.
Normally, a can body is sealed when a can end is double-seamed on the can body by a double end seamer or seaming machine. There are known various double end seaming machines with different processing capabilities and different seaming mechanisms. However, any double end seaming machines are composed mainly of a lifter, a seaming chuck, and a seaming roll which make up a seaming mechanism.
The lifter holds the bottom end of a can body. When a can body filled with contents and carrying a can end is supplied onto the lifter, the lifter is elevated until the can end is held by seaming chuck which is positioned above the lifter. The can end is fitted in and pressed against the can body by the seaming chuck. The can end and the can body are now securely held by the seaming chuck and the lifter. While the can end is being seamed, the lifter serves as a cushion for pressing the can end and the can body against the seaming chuck under a certain degree of resiliency. Adjusting the lifter cushion resiliency plays a vital role in adjusting the strength with which the can end is seamed on the can body.
The seaming chuck is held in intimate contact with the can end in the can end double seaming machine. During the seaming process, the seaming chuck holds the can end and the can body in cooperation with the lifter, and is simultaneously subjected to the pressure from the seaming roll.
The seaming roll comprises a first seaming roll and a second seaming roll. The first and second seaming rolls have respective grooves of different contours. Generally, the groove of the first seaming roll is narrower and deeper, and the groove of the second seaming roll is wider and shallower.
The lifter, the seaming chuck, and the seaming roll (first and second seaming rolls) coact to overlap and bend a flange of the can body and a curl of the can end until the end curl is fully tucked up beneath the body flange. The sealing of the seamed structure is enhanced by a sealing compound applied between the end curl and the body flange.
Depending on the processing capacity of the can end double seaming machine, the lifter, the seaming chuck, and the seaming roll are adjustably positioned relatively to each other to make it possible to double-seam can ends of various cans having different diameters and heights or lengths.
Various factors which affect the double-seaming of cans include the thickness and temper of can sheets such as of tin, aluminum, the contours of the seaming roll grooves, the gradient of the seaming chuck, the configurations of the end curl and the body flange, and the coated conditions of the sealing compound, among other things. The most influential element is the adjustment of a relative positional relationship between the seaming roll, the lifter, and the seaming chuck, and a lot of skill is required to carry out such positional adjustment.
More specifically, in order to double-seam a can end on a can body with a can end double seaming machine, it is necessary that a seaming check and a seaming roll, which match the can end and the can body to be seamed together, be set on a seaming head that is vertically mounted on a base, and the seaming head be positioned into conformity with the height of the can body on a lifter placed on the base. To meet the above requirement, the seaming head with the seaming chuck and the seaming roll set thereon is vertically movable with respect to the lifter on the base.
The seaming head can be vertically moved, i.e., lifted and lowered, by a rotor rotatably threaded in a threaded hole which is defined in an upper portion of a support column that is vertically mounted on the base, and a manually operable handle operably coupled to the rotor through a gearing for rotating the rotor.
To set the seaming chuck and the seaming roll on the seaming head, the handle is manually turned to rotate the rotor for thereby elevating the seaming head. Then, the seaming chuck and the seaming roll are mounted on the seaming head as desired. Thereafter, the handle is manually turned again to lower the seaming head into a desired seaming position.
At this time, the lifter on the base and the seaming chuck and the seaming roll set on the seaming head should be spaced apart at a highly accurate distance corresponding to the height or length of the can body on which the can end is to be seamed. The gear ratio of the gearing is selected such that the seaming head is vertically moved a relatively small distance in response to one revolution of the handle. Consequently, the vertical movement of the seaming head can be finely adjusted by the handle. When lowering the seaming head to the desired seaming position, the handle is turned to finely adjust the vertical position of the seaming head while measuring the distance between the lifter and the seaming chuck and the seaming roll with a microgage or the like.
However, the use of the manually operable handle to lift or lower the seaming head into the desired seaming position is disadvantageous in that it takes a long period of time to reach the desired seaming position because the distance that the seaming head moves per revolution of the handle is considerably small, and also in that the adjustment of the seaming head position needs a skillful operator.
While modern can end double-seaming machines operate at high speed for increased productivity, the entire process involving the manual positional adjustment is inefficient because it is time-consuming to position the seaming chuck and the seaming roll for double-seaming operation.